Surface inspection instrument and surface inspection method

ABSTRACT

By using a surface inspection apparatus comprising a light source  11  for applying a light to a surface of an object  2  to be measured, an objective lens  12  opposite to the surface of the object  2  to be measured and for receiving a reflected light applied from the light source  11  and reflected on the surface of the object  2  to be measured, light detection means  13  for detecting a component incident on the objective lens  12  from a parallel direction with its optical axis in the reflected light passing through this objective lens  12  and obtaining its light quantity, and a slit  29  provided in the optical path between the objective lens  12  and light detection means  13 , because the light detection extent in the surface of the object  2  to be measured can be narrowed with the slit  29 , its surface condition can be measured with a good accuracy independently of the shape of the object to be measured.

TECHNICAL FIELD

[0001] The present invention relates to a surface inspection apparatusand a surface inspection method, particularly to a surface inspectionapparatus and a surface inspection method for measuring surfaceconditions of automobile parts, OA apparatus, household electricappliances or the like.

BACKGROUND ART

[0002] In fields of trim parts of automobile, OA, domesticelectrification or the like, the level of requirement for physicalproperties of the surfaces of products concerning their externalappearances, in concrete terms, injuries, unevenness in height,unevenness in gloss, unevenness in color, and so forth, has becomeseverer year by year. In particular, in products made of syntheticresins, in addition to the above-described various properties, theexternal appearance of a weld line, the external appearance of flowmarks, stress whitening, and so forth, are greatly concerned in theircommodity values.

[0003] The surface condition of such a product is hitherto appraised byperforming a sensuous test, in which a classification is made on eyeobservation. In the sensuous test, however, the result of the test isobtained only in a rank on each appraisal item, and minute informationon the surface condition, that is, information at the same level as astate of seeing with the naked eye can not be preserved, so it is ahindrance to quality control and material development.

[0004] In order to solve such a problem, it has been done to keep thesurface condition of a product with a photograph or the like, but it isnot considered objective data because its contrast varies according tophotographing conditions, printing conditions, and so forth, so a methodand an apparatus in which the surface condition of a product or amaterial can be accurately evaluated or measured have been desiredearnestly.

[0005] On the other hand, as a method for measuring the surfacecondition of a synthetic resin material, the present applicant proposeda method for measuring the degree of whitening by an injury in thesurface of the material (Japanese Patent Publication No. 52160/1995).This method is a method in which an injury of a predetermined shape isinflicted on a sample made of a synthetic resin, the injured whiteningportion is irradiated with a light in dark-field illumination, and thelight quantity of the component parallel with the optical axis of theobjective lens in diffusedly reflected rays of the light is measured tomeasure the injury whitening degree. By changing the magnification ofthe objective lens according to the size of the injury, the lightdetection extent, that is, the extent in the surface of the samplesubject to the measurement of the reflected light is controlled.

[0006] This method is useful for a material test in material developmentor the like, but has a problem that it can not be applied to surfaceinspection of products in quality control. That is, in this method,because an injury of a predetermined shape must be inflicted on a samplefor measurement, the surface condition of the product can not beevaluated as it is, and further, because only the portion of the injuryof the predetermined shape is measured due to the low detectionaccuracy, the surface condition of the whole of the object to bemeasured including the portion other than the injury can not bemeasured.

[0007] Besides, because an objective lens of a high magnification isused to decrease the detection extent when the whitening degree of aminute injury is measured, in case of a sample having a complicatedshape, or the like, if the injury varies in position, a measurementerror arises due to a divergence of the focus so a highly accuratemeasurement can not be realized. If an objective lens of a lowmagnification is used in order to decrease such a divergence of thefocus, the peripheral portion of the injury is included in the detectionextent, and so there is a problem that the reflected light from theinjury can not be detected with a good accuracy.

DISCLOSURE OF THE INVENTION

[0008] It is an object of the present invention to provide a surfaceinspection apparatus and a surface inspection method in which thesurface condition can be measured with a good accuracy independently ofthe shape of an object to be measured, and which can be applied also tosurface inspection of products.

[0009] A surface inspection apparatus of the present invention ischaracterized by comprising a light source for applying a light to asurface of an object to be measured, an objective lens opposite to thesurface of the object to be measured and for receiving a reflected lightapplied from the light source and reflected on the surface of the objectto be measured, light detection means for detecting a component incidenton the corresponding objective lens from a parallel direction with itsoptical axis in the reflected light passing through this objective lensand obtaining its light quantity, and a slit provided in the opticalpath between the objective lens and light detection means.

[0010] In the present invention, the light applied from the light sourceis reflected on the surface of the object to be measured, and thereflected light passes through the objective lens. When the reflectedlight is incident on the objective lens, the reflected light incident inparallel with the optical axis of the objective lens is incident on theslit after passing through the objective lens, and only the light havingpassed through the opening of this slit is introduced to the lightdetection means to obtain its light quantity.

[0011] In this manner, because the slit is provided in the light pathbetween the objective lens and the light detection means, since only thecomponent having passed through the opening of the slit in the reflectedlight reflected in the parallel direction with the optical axis of theobjective lens can be taken out and detected, the detection extent ofthe reflected light in the surface of the object to be measured, namely,the light detection extent can be restricted by the opening of the slit.Accordingly, because the reflected light within the extent limited bynarrowing the light detection extent with the objective lens and theslit can be taken out and its light quantity can be obtained, thesurface condition of the aimed external appearance can be measuredexactly and with a high accuracy.

[0012] Further, when the surface condition of the object to be measuredof a complicated shape is measured, in case of using the objective lensof a low magnification for preventing a divergence of the focus, becausethe detection extent in the surface of the object to be measured can berestricted by the slit, since the surface of the object to be measuredcan be finely divided into a plurality of light detection extents anddetected, the surface condition of the object to be measured can bemeasured with a good accuracy.

[0013] Because a superior detection accuracy can be obtained in thismanner, not only the conventional degree of whitening of an injury butalso a difference in the surface condition due to color, unevenness inheight, or the like can be measured, and because the whole of thesurface of the object to be measured including an uninjured portion canbe measured, in addition to that an evaluation result corresponding tothe external appearance of the object to be measured can be obtained,since it is avoided to inflict a predetermined injury on the surface ofthe object to be measured for measurement as a conventional manner, itcan be applied to not only a surface inspection of a material but also asurface inspection in quality inspection of products.

[0014] Besides, when the object to be measured is evaluated withscanning, it is desirable to narrow the measurement area, that is, thelight detection extent. At this time, because there is a fear ofmovement of focus with scanning, it is preferable for suppressing themovement of focus to narrow the light detection extent by using theobjective lens of a magnification as low as possible and decreasing theopening of the slit.

[0015] Besides, because the objective lens of a lower magnification getsnearer to the external appearance of eye observation, a high correlationwith the eye observation result can be obtained. Accordingly, it isdesirable to use the objective lens of a low magnification, for example,not more than 10, particularly, 1 to 5.

[0016] Here, when the magnification is 1, a plane glass board merelytransmitting light, an optical fiber cable or the like may be used asthe objective lens, or the objective lens itself may not be used.

[0017] That is, it is a surface inspection apparatus characterized bycomprising a light source for applying a light to a surface of an objectto be measured, a tubular member, for example, an optical fiber cableopposite to the surface of said object to be measured and for receivinga reflected light applied from said light source and reflected on thesurface of said object to be measured, light detection means fordetecting a component incident on this tubular member from a specifieddirection in the reflected light and obtaining its light quantity, and aslit provided in the optical path between said tubular member and lightdetection means.

[0018] Further, in the apparatus of the present invention, if thespectral characteristic of the light source and the spectral sensitivityof the light detection means are provided into standard ones byselecting the light source and the light detection means, the lightquantity can be obtained as a standardized value such ascolor-difference and lightness.

[0019] In the above, it is desirable that illumination switchover meansis provided in the light path between the light source and object to bemeasured, and this illumination switchover means is to switch overbright-field illumination in which the light from the light source ismade parallel with the optical axis of the objective lens and applied tothe object to be measured through the objective lens, and dark-fieldillumination in which the light from the light source is made ringlikeand applied obliquely with respect to the optical axis of the objectivelens such that there is a focus on the surface of the object to bemeasured.

[0020] In this case, with the illumination switchover means, by properlyusing bright-field illumination and dark-field illumination according tothe surface condition of the object to be measured or an aimed item tothe surface condition, the surface condition of the object to bemeasured can be measured with a higher accuracy.

[0021] For example, in case of the object to be measured being made of asynthetic resin, when it is inspected on the presence of an injury, thesize of the injury or the like, because the light becomes easier to bediffusedly reflected on the injury or the like by using dark-fieldillumination, in which the light is applied from an oblique direction,the detected light quantity increases and decreases greatly according tothe injury, and a superior correlation with the eye observation resultcan be obtained. On the other hand, when it is inspected on unevennessin lightness, unevenness in gloss, the external appearance of a weld,the external appearance of flow marks, or the like, if bright-fieldillumination and dark-field illumination are selected according to theeye observation and used, a highly accurate inspection resultcorresponding to the eye observation can be obtained on each item.

[0022] Besides, in dark-field illumination, because the surface of theobject to be measured is irradiated with the light in a ringlike mannerfrom all directions, a measurement error due to difference inirradiation direction can be dissolved and a superior detection resultcorrelated with the eye observation result can be obtained. That is, ifthe light is applied to the object to be measured only from onedirection, because inferiority in the external appearance or the likehas directivity in general, there is a case that the detected lightquantity of the reflected light is different from the case of applyingthe light from the other direction, besides, because the direction ofviewing the object to be measured in the eye observation judgement isnot always fixed, by applying the light in the ringlike manner, scatterin data according to irradiation directions can be dissolved.

[0023] Further, when an abnormal portion in the surface of the object tobe measured is measured by using dark-field illumination, it isdesirable to set up the irradiation angle with the light with respect tothe optical axis of the objective lens on the basis of the eyeobservation result. In concrete words, it is desirable that the abnormalportion of the object to be measured is observed with the naked eye withvarying the angle, an angle condition in which a difference from thenormal portion can be notably distinguished is selected, and thisselected angle is used as the irradiation angle with the light. Thereby,because the surface condition can be observed under the same conditionas the eye observation, a correlation with the eye observation resultcan be obtained.

[0024] It is desirable that the size of the opening of theabove-mentioned slit is changeable.

[0025] Thereby, because the light detection extent in the surface of theobject to be measured can be voluntarily controlled according to thesurface condition of the object to be measured or the like bycontrolling the size of the opening of the slit, a more highly accurateinspection can be realized.

[0026] As the slit, for example, one having a circular opening can beused, and in this case, the diameter of the opening of the slit isdesirably 0.2 to 30 mm. If the diameter of the opening of the slit isless than 0.2 mm, the light introduced into the light detection part isinsufficient and there arises a fear that it becomes hard to measure.

[0027] Besides, when one on the surface of which uneven crimps are givenis used as the object to be measured, it is preferable to broaden thelight detection extent by increasing the diameter of the opening of theslit because a variation in measured value decreases.

[0028] Further, it is desirable that the above-mentioned light detectionmeans comprises calculation means for converting the light quantity ofthe light having passed through the slit on the basis of a lightquantity detected when a standard sample is used as the object to bemeasured.

[0029] Here, the standard sample is the sample used as a standardrespectively in properties liked to inspect on the object to bemeasured, in concrete words, lightness, degree of white, colordifference, or the like, for example, a standard sample that is made incommon on the basis of a standard color chip of color such as whitestandard board and Munsell chroma, a standard sample set upindividually, the normal portion in the object to be measured, or thelike. This standard sample may be properly selected according to theevaluation item.

[0030] If such calculation means is provided, the light quantitydetected on the object to be measured can be obtained as a relativevalue based on the light quantity of the standard sample. That is, notonly an absolute measurement but also a comparative measurement can beperformed. Accordingly, the inspection result can be obtained with agood reproducibility as a value near to the eye observation and easy tounderstand.

[0031] Besides, if one of a good eye observation result is used as thestandard sample, because a relative inspection result based on thisstandard sample is obtained, the object to be measured can be evaluatedwith ease.

[0032] Further, when the inspections are performed with varying themeasurement conditions, by using the same standard sample under eachmeasurement condition and converting the light quantity of the object tobe measured on the basis of the light quantity of this standard sample,because an error in the inspection result due to the difference in themeasurement condition can be dissolved, an accurate inspection result isobtained.

[0033] On the other hand, a surface inspection method of the presentinvention is characterized in that a surface of an object to be measuredis irradiated with a light and the irradiation light is reflected on thesurface of the object to be measured, in this reflected light, acomponent parallel with the optical axis of an objective lens providedoppositely to the object to be measured is made incident on a slitthrough the objective lens, in this incident light, only a componenthaving passed through an opening of said slit is received, and the lightquantity of this received light is obtained.

[0034] In the present invention, since only the component having passedthrough the opening of the slit in the reflected light reflected in theparallel direction with the optical axis of the objective lens can betaken out and detected, the detection extent of the reflected light inthe surface of the object to be measured, namely, the light detectionextent can be restricted by the opening of the slit. Accordingly,because the reflected light within the extent limited by narrowing thelight detection extent with the objective lens and the slit can be takenout and its light quantity can be obtained, the surface condition can bemeasured exactly and with a high accuracy.

[0035] Besides, even in case of using the objective lens of a lowmagnification, because the detection extent in the surface of the objectto be measured can be restricted by the slit, the surface condition ofthe object to be measured can be measured with a good accuracy.

[0036] Further, because a superior detection accuracy can be obtained,not only the conventional degree of whitening of an injury but also evena shining injury (injury conspicuous due to increase in gloss of theinjured portion, particularly, injury conspicuous upon holding theobject to be measured to the light) can be measured. Besides, also adifference in the surface condition due to color, unevenness in height,or the like can be measured, and because the whole of the surface of theobject to be measured including an uninjured portion can be measured, anevaluation result corresponding to the external appearance of the objectto be measured can be obtained.

[0037] Further, since it is avoided to inflict a predetermined injury onthe surface of the object to be measured for measurement as aconventional manner, it can be applied to not only a surface inspectionof a material but also a surface inspection in quality inspection ofproducts.

[0038] It is desirable that the light detection extent in the surface ofthe object to be measured is controlled by changing the size of theopening of the above-mentioned slit and the magnification of theobjective lens, respectively.

[0039] Because the light detection extent in the surface of the objectto be measured can be voluntarily controlled according to the surfacecondition of the object to be measured or the like by combining the sizeof the opening of the slit and the magnification of the objective lensin this manner, a more highly accurate inspection can be realized.

[0040] Further, it is desirable that the light quantity of the receivedlight is converted on the basis of a light quantity detected when astandard sample is used as the object to be measured.

[0041] Thereby, because the light quantity of the light received on theobject to be measured can be obtained as a relative value based on thestandard sample, the reliability in the value of each measurement ishigh and the inspection result can be obtained with a goodreproducibility as a value near to the eye observation and easy tounderstand.

[0042] Besides, if one of a good eye observation result is used as thestandard sample, because a relative inspection result based on thisstandard sample is obtained, the object to be measured can be evaluatedwith ease.

[0043] Further, when the inspections are performed with varying themeasurement conditions, by using the same standard sample under eachmeasurement condition and converting the light quantity of the object tobe measured on the basis of the light quantity of this standard sample,because an error in the inspection result due to the difference in themeasurement condition can be dissolved, an accurate inspection result isobtained.

[0044] The irradiation angle with the light to the object to be measuredmay be changed according to the surface condition of the object to bemeasured.

[0045] There is no particular limit in this irradiation angle, and itmay be voluntarily set up according to the object of the inspection andthe surface condition of the object to be measured within a range of 0to 45 degrees with respect to the optical axis of the objective lens.

[0046] By controlling the irradiation angle with the light in thismanner, the surface condition of the object to be measured can bemeasured with a higher accuracy.

[0047] For example, when unevenness in gloss, the external appearance ofa weld, flow marks, the presence of an injury, unevenness in height, orthe like of the object to be measured made of a synthetic resin, if theirradiation angle with the light is selected by observing the object tobe measured with the naked eye with varying the angle, a highly accurateinspection result corresponding to the eye observation can be obtainedon each item.

BRIEF DESCRIPTION OF THE DRAWINGS

[0048]FIG. 1 is a view showing an embodiment of the present inventionwith its partial section.

[0049]FIG. 2 is a perspective view showing illumination switchover meansof the above embodiment.

[0050]FIG. 3 is a block diagram showing light detection means of theabove embodiment.

[0051]FIG. 4 is a view showing a result that the external appearance ofa weld line is inspected with the surface inspection apparatus of theabove embodiment.

DESCRIPTION OF REFERENCES

[0052]1 surface inspection apparatus

[0053]2 object to be measured

[0054]11 light source

[0055]12 objective lens

[0056]13 light detection means

[0057]14 bright/dark-field switchover slide (illumination switchovermeans)

[0058]29 slit

[0059]29A, 29B opening

[0060]42 photoelectric conversion means

[0061]44 calculation means

BEST MODE FOR CARRYING OUT THE INVENTION

[0062] Hereinafter, an embodiment of the present invention will bedescribed based on drawings.

[0063] In FIG. 1, a surface inspection apparatus 1 of this embodiment isshown. This surface inspection apparatus 1 comprises a light source 11for applying a light to a surface of an object 2 to be measured, anobjective lens 12 provided at the position opposite to the surface ofthe object 2 to be measured, and light detection means 13 for detectinga component incident on this objective lens 12 in a parallel directionwith its optical axis to obtain the light quantity. In concrete terms,it is constructed by the manner that the light detection means 13 isconnected to a polarizing microscope 3 of a reflected-illumination typeincluding the light source 11 and the objective lens 12.

[0064] The microscope main body 30 of the polarizing microscope 3comprises a tube 31 for vertical light path provided vertically and atube 32 for illumination light path extending horizontally from the tube31 for vertical light path. An objective lens barrel 33 is attached tothe lower end portion of the tube 31 for vertical light path. Thisobjective lens barrel 33 is attached perpendicularly to the axial lineof the tube 32 for illumination light path.

[0065] In the interior of this objective lens barrel 33, the objectivelens 12 is received, and a ringlike lens 25 for dark-field illumination,which will be described later, is received on the outer circumference ofthe objective lens 12. These objective lens 12 and lens 25 fordark-field illumination are put in with selectively combining one havinga predetermined magnification and one having a predetermined refractiveindex, respectively. For such objective lens barrels 33, plural kinds ofvarious magnifications of the objective lenses 12 and various refractiveindices of the lenses 25 for dark-field illumination are provided, andby selectively mounting the objective lens barrel 33 on the tube 31 forvertical light path, the magnification of the objective lens 12 and therefractive index of the lens 25 for dark-field illumination inmeasurement can be adjusted.

[0066] Below this objective lens barrel 33, a stage 21 for putting theobject 2 to be measured is provided. This stage 21 is disposed on theoptical axis of the objective lens 12, and set so as to be movablehorizontally and vertically.

[0067] The light source 11 is set on an axis perpendicularlyintersecting the optical axis of the objective lens 12 in the interiorof the tube 32 for illumination light path. On this axis, a collimatelens 22 for making a light from the light source 11 parallel raysperpendicularly intersecting the optical axis of the objective lens 12is disposed.

[0068] Besides, at the position of an intersecting point between theoptical axis of the light from the light source 11 and the optical axisof the objective lens 12 in the tube 31 for vertical light path, abright/dark-field switchover slide 14, which is illumination switchovermeans for applying the light from the light source 11 to the object 2 tobe measured as dark-field illumination or bright-field illumination, isset.

[0069] As also shown in FIG. 2, this bright/dark-field switchover slide14 is attached such that it can slide in the direction perpendicularlyintersecting the optical axis of the light from the light source 11 andthe optical axis of the objective lens 12. Along this slide direction, acircular half-mirror portion 23 for bright-field illumination and aringlike fully-reflective-mirror portion 24 the inner portion of whichis a light-pass portion 24A are provided in parallel. Besides, on theperiphery of the objective lens 12, the ringlike dark-field illuminationlens 25 is provided, and it is constructed such that the light reflectedon the ringlike fully-reflective-mirror portion 24 in the direction ofthe optical axis of the objective lens 12 is applied from an obliquedirection in order that there is a focus on the surface of the object 2to be measured. For these dark-field illumination lenses 25, pluralkinds of various refractive indices are provided, and by properlyselecting and using these, the irradiation angle to the surface of theobject 2 to be measured, namely, the irradiation angle with the lightwith respect to the optical axis of the objective lens 12 can beadjusted.

[0070] In such a polarizing microscope 3, by sliding thebright/dark-field switchover slide 14, bright-field illumination, inwhich the object 2 to be measured is irradiated with the light at theirradiation angle of zero degrees, and dark-field illumination, in whichthe object 2 to be measured is irradiated with the light at an obliqueirradiation angle with respect to the optical axis of the objective lens12, are switched over.

[0071] That is, as shown in FIG. 1, when the ringlikefully-reflective-mirror portion 24 for dark-field illumination isswitched on the optical axis, only the light applied to the ringlikefully-reflective-mirror portion 24 in parallel rays from the collimatelens 22 is reflected to be formed into a ring shape and parallel withthe optical axis of the objective lens 12, enters the dark-fieldillumination lens 25, and is refracted by an oblique angle with respectto the optical axis of the objective lens 12, for example, 45 degrees tobe applied to the surface of the object 2 to be measured.

[0072] On the other hand, when the circular half-mirror portion 23 forbright-field illumination (refer to FIG. 2) is switched on the opticalaxis, only the light applied to the circular half-mirror portion 23 inparallel rays from the collimate lens 22 is reflected to be parallelwith the optical axis of the objective lens 12, and applied through theobjective lens 12 to the surface of the object 2 to be measured at theirradiation angle of zero degrees with respect to the optical axis ofthe objective lens 12.

[0073] Such a bright/dark-field switchover slide 14 is disposed on thesame axial line as the objective lens 12 and stage 21. Above thisbright/dark-field switchover slide 14, a barrel including an eyepiecenot shown and the light detection means 13 are provided. These barrel(omitted in the drawing) and light detection means 13 are disposed onthe optical axis of the objective lens 12.

[0074] In the apparatus 1 of this embodiment, the irradiation lightapplied to the surface of the object 2 to be measured from the lightsource 11 through the bright/dark-field switchover slide 14 is reflectedon the surface of the object 2 to be measured to enter the objectivelens 12. The component parallel with the optical axis of the objectivelens 12 in the reflected light incident on this objective lens 12 isreceived by the light detection means 13.

[0075] In the light path between this light detection means 13 and theobjective lens 12, in concrete words, between the light detection means13 and the bright/dark-field switchover slide 14, a disclike slit 29 isset. This slit 29 is attached so as to be horizontally rotatable aroundits center. The slit 29 has a plurality of openings 29A and 29Bdifferent in size along its circumferential direction, and is attachedsuch that these openings 29A and 29B are positioned on the optical axisof the objective lens 12 by rotation of the slit 29, respectively.

[0076] Thereby, by rotating the slit 29, the sizes of the openings 29Aand 29B of the slit 29 on the optical axis of the objective lens 12 arechanged to introduce only the light P having passed through the openings29A and 29B on the optical axis to the light detection means 13.

[0077] Besides, in order to be operated for rotation from the outside ofthe microscope main body 30, the slit 29 is set such that its partprojects outward beyond the tube 31 for vertical light path.

[0078] The shapes of the openings 29A and 29B of the slit 29 are notparticularly limited and they may be circular ones or rectangular ones.

[0079] The above-described barrel (omitted in the drawing) including theeyepiece is provided below this slit 29, the size of the opening of theslit 29 is indicated in the visual field when the surface of the object2 to be measured is observed through the eyepiece. Accordingly, as thesurface of the object 2 to be measured is observed, the optimum openingof the slit 29 can be selected.

[0080] On the other hand, as shown in FIG. 3, the light detection means13 is for receiving the light P having passed through the slit 29 toobtain its light quantity, and at need, converting this light quantitybased on the light quantity of a standard sample.

[0081] This light detection means 13 comprises input means 41 forsetting up the light quantity of the standard sample as a standardvalue, photoelectric conversion means 42 for converting the lightquantity of the received light into an electric current value, an A/Dconverter 43 for digitizing the electric current value from thisphotoelectric conversion means 42, calculation means 44 for convertingthis digitized signal into a predetermined value. Display means 45 andmemory means 46 are connected to this calculation means 44, and thereby,based on a setting-up command of the standard value from the input means41, the light quantity of the object to be measured is calculated by thecalculation means 44 according to data and a program stored in thememory means 46, and digitally displayed by the display means 45.

[0082] Next, a surface inspection method of this embodiment using thesurface inspection apparatus 1 will be described.

[0083] First, the object 2 to be measured is put on the stage 21, and asthe surface of the object 2 to be measured is observed through theeyepiece (omitted in the drawing), the magnification of the objectivelens 12 is selected by changing the objective barrel 33, and the slit 29is rotated to select the openings 29A and 29B disposed on the opticalaxis of the objective lens 12, and the light detection extent in thesurface of the object 2 to be measured is controlled. In such a controlof the light detection extent, the light detection extent restricted bythe objective lens 12 is further restricted by the slit 29.

[0084] On the other hand, by sliding the bright/dark-field switchoverslide 14 according to aimed items on the surface condition of the object2 to be measured and the surface condition of the object 2 to bemeasured, illumination from the light source 11 is switched tobright-field illumination or dark-field illumination.

[0085] For example, in case of the object 2 to be measured being made ofa synthetic resin, when it is inspected on items such as the presence ofan injury and the size of the injury, in general, because the light iseasier to be diffusedly reflected on the portion of the injury or thelike when the light is applied from an oblique direction, dark-fieldillumination is used. On the other hand, when it is inspected on itemssuch as unevenness in gloss, the external appearance of a weld, and flowmarks, an angle at which a difference from the normal portion isobviously observed with the naked eye is selected, and bright-fieldillumination is used when this angle is zero degrees and dark-fieldillumination is used when it is an angle other than zero degrees. Thelight quantity is thereby accurately reflective of the surface conditionof the object 2 to be measured on each item, and an inspection resultcorresponding to the eye observation can be obtained.

[0086] At this time, the irradiation angle with the light in dark-fieldillumination is made to correspond to the eye observation by setting upthe refractive index of the lens 25 for dark-field illumination on thebasis of the selected angle, and the irradiation angle is, for example,45 degrees. Setting up the refractive index of the lens 25 fordark-field illumination is carried out by mounting the objective lensbarrel 33 with the lens 25 for dark-field illumination of a desiredrefractive index onto the tube 31 for vertical light path.

[0087] When the light is applied from the light source 11, thisirradiation light passes through the collimate lens 22 to be parallelrays, and is applied to the surface of the object 2 to be measuredthrough the bright/dark-field switchover slide 14. This irradiationlight is reflected on the surface of the object 2 to be measured, thecomponent parallel with the optical axis of the objective lens 12 inthis reflected light passes through the objective lens 12 to be incidenton the slit 29, and only the component having passed through theopenings 29A and 29B of the slit 29 in this incident light is detectedby the photoelectric conversion means 42 of the light detection means 13to convert its light quantity into an electric current value. Thiselectric current value is digitized by the A/D converter 43, and when acalculation process is not performed, the electric current value isdigitally displayed by the display means 45 as it is.

[0088] At this time, because the reflection angle of the light reflectedon the surface of the object 2 to be measured, the intensity of thereflected light (reflectance) and the like vary according to the surfacecondition of the object 2 to be measured, the light quantity detected bythe light detection means 13, namely, the displayed electric currentvalue varies according to the surface condition of the object 2 to bemeasured.

[0089] For example, when there is a whitening injury (a crack due tosurface chapping) in the surface of the object 2 to be measured, becausethe light applied to the portion of the injury is diffusedly reflected,between the portion of the injury and the portion where no injury ispresent, there is a difference in the light quantity incident on theobjective lens 12 and passing through the slit 29, namely, in thedetected light quantity.

[0090] Besides, when the color of the surface of the object 2 to bemeasured, in concrete terms, the hue, the lightness, the chroma or thelike is variant, because the reflectance of the light varies, thedetected light quantity varies according to the color of the surface ofthe object 2 to be measured.

[0091] When such an inspection is performed to a certain extent in thesurface of the object 2 to be measured or the whole of the surface,namely, when it is evaluated with scanning, the inspection is performedas the object 2 to be measured is being moved by horizontally moving thestage 21 upon measurement, and the light is processed with sampling atregular periods in the light detection means 13. At this time, the stage21 may be moved continuously or intermittently.

[0092] On the other hand, in case that the light quantity detected inthe inspection of the object 2 to be measured is converted on the basisof the light quantity detected when the standard sample is used as theobject to be measured, the surface condition of the standard sample isinspected beforehand like the above-described inspection of the object 2to be measured, its light quantity is set up as the standard value bythe input means 41 and stored in the memory means 46.

[0093] By the input means 41, it is set up to process to convert thelight quantity of the object 2 to be measured on the basis of the storedstandard value, and the surface condition of the object 2 to be measuredis inspected. So, in the light detection means 13, the light quantity ofthe light received by the photoelectric conversion means 42 is convertedinto an electric current value, and the electric current value isdigitized by the A/D converter 43 to be input to the calculation means44. In this calculation means 44, the digitized electric current valueis compared with the standard value stored in the memory means 46 to becalculated into a relative value, and this value is digitally displayedby the display means 45.

[0094] This standard sample is properly selected according to aimeditems on the surface condition of the object 2 to be measured, an objectof the inspection or the like.

[0095] For example, in case of a quality inspection of products or aninspection on an abnormal sample, a normal sample is used as thestandard sample and a comparison result with the normal sample can beoutput. In concrete words, when a synthetic resin product is inspectedwith aiming items such as the lightness, the glossiness, the externalappearance of a weld, and the external appearance of flow marks, byinspecting the product as the object to be inspected or the abnormalsample with the standard sample of the product with a good eyeobservation result on these items, the light quantities of thesereflected lights are displayed as comparison results with the lightquantity of the good product.

[0096] Besides, standardized one which becomes the base on an item aimedof inspection may be used as the standard sample. For example, when thecolor of the sample is evaluated, by using one generally used as astandard of object color, in concrete words, a color sample based on astandard chroma such as Munsell chroma as the standard sample, the lightquantity of the object 2 to be measured as the inspection object isdisplayed as a difference in color from the standard sample.

[0097] Further, in one object 2 to be measured, when the evenness in itssurface condition, in concrete words, unevenness in lightness,unevenness in gloss, unevenness in height, unevenness in color or thelike is inspected, a predetermined portion in its surface may be used asthe standard sample and the other portion may be measured with thestandard value of the light quantity detected on this portion used asthe standard sample. In this case, the detected light quantity is outputas a difference from the light quantity of the portion used as thestandard sample.

[0098] According to this embodiment as described above, there are thefollowing effects.

[0099] That is, because the slit 29 is provided in the light pathbetween the objective lens 12 and the light detection means 13, sinceonly the component having passed through the opening 29A or 29B of theslit 29 in the reflected light reflected in the parallel direction withthe optical axis of the objective lens 12 can be taken out and detected,the detection extent of the reflected light in the surface of the object2 to be measured, namely, the light detection extent can be restrictedby the opening 29A or 29B of the slit 29. Accordingly, because thereflected light within the extent limited by narrowing the lightdetection extent with the objective lens 12 and the slit 29 can be takenout and its light quantity can be obtained, the surface condition can bemeasured exactly and with a high accuracy.

[0100] In particular, when the surface condition of the object to bemeasured of a complicated shape is measured, in case of using theobjective lens 12 of a low magnification for preventing a divergence ofthe focus, even in case of using no objective lens, because thedetection extent in the surface of the object 2 to be measured can berestricted by the slit 29, since the surface of the object 2 to bemeasured can be finely divided into a plurality of detection extents anddetected in the low magnification as it is, the surface condition of theobject 2 to be measured can be measured with a good accuracy.

[0101] Further, because a superior detection accuracy can be obtained,not only the degree of whitening of an injury but also a difference inthe surface condition due to color, gloss, unevenness in height, or thelike can be measured, and because the whole of the surface of the object2 to be measured can be measured, in addition to that an evaluationresult corresponding to the external appearance of the object 2 to bemeasured can be obtained, since it is avoided to inflict a predeterminedinjury on the surface of the object 2 to be measured for measurement asa conventional manner, it can be applied to not only a surfaceinspection of a material but also a surface inspection in qualityinspection of products.

[0102] Because the bright/dark-field switchover slide 14 is provided inthe light path between the light source 11 and the object 2 to bemeasured, by properly using bright-field illumination and dark-fieldillumination correspondingly to the observation angle selected byobserving the surface condition of the object 2 to be measured on adesired item with the naked eye, the surface condition of the object 2to be measured can be measured with a higher accuracy.

[0103] Besides, in dark-field illumination, because the surface of theobject 2 to be measured is irradiated with the light in a ringlikemanner from all directions, a measurement error due to difference inirradiation direction can be dissolved and a superior detection resultcorrelated with the eye observation result can be obtained. That is, ifthe light is applied to the object 2 to be measured only from onedirection, there is a case that the detected light quantity is differentfrom the case of applying the light from the other direction, besides,because the direction of viewing the object 2 to be measured in the eyeobservation judgement is not always fixed, by applying the light in theringlike manner, scatter in data according to irradiation directions canbe dissolved and the surface condition can be observed under the similarconditions to those of the eye observation.

[0104] By changing the magnification of the objective lens 12 and thesizes of the openings 29A and 29B of the slit 29, respectively, becausethe light detection extent in the surface of the object 2 to be measuredcan be controlled, an inspection with a higher accuracy can be realized.

[0105] Further, because the light detection means 13 has the calculationmeans 44, since the light quantity detected on the object 2 to bemeasured can be obtained as a value based on the light quantity of thestandard sample, the inspection result can be obtained as the valueclose to the eye observation result and easy to understand.

[0106] Besides, by using one of a good eye observation result as thestandard sample, because a relative inspection result based on thisstandard sample can be obtained, the object 2 to be measured can beevaluated with ease.

[0107] Further, even in case of inspecting with varying the measurementconditions, by using the same standard sample under each measurementcondition and converting the light quantity of the object 2 to bemeasured on the basis of the light quantity of this standard sample,because error in inspection result due to difference in measurementcondition can be dissolved, an accurate inspection result can beobtained.

[0108] Besides, because the surface inspection apparatus 1 isconstructed by using the already present polarizing microscope 3, onlyby setting the slit 29 in the polarizing microscope 3 and connecting itto the light detection means 13, the apparatus 1 can be assembled withease and at a low cost.

[0109] The present invention is not limited to the above embodiment, andcontains other constitutions and the like that can attain the object ofthe present invention, and such modifications as shown below are alsocontained by the present invention.

[0110] Besides, although the slit in the above embodiment is formed intoa disclike shape, it is not limited to this, for example, the slit maybe formed into a beltlike shape, openings may be provided in parallelalong its longitudinal direction, and the opening to be disposed on theoptical axis of the objective lens may be selected by sliding the slitalong the longitudinal direction, or a plurality of slits different insize of opening may be provided and the size of the opening on theoptical axis may be changed by properly selecting and mounting thisslit. Besides, the opening of the slit may be formed at a position beingoff the optical axis of the objective lens at need.

[0111] Although bright-field illumination and dark-field illuminationare switched over by using the bright/dark-field slide 14 in the aboveembodiment, illumination switchover means is not limited to theconstruction using the bright/dark-field slide 14, for example, aconstruction using a slide different in shape from the slide 14 of theabove embodiment may be employed, or fibers for illumination may bedisposed annularly on the periphery of the objective lens to makedark-field illumination. After all, if bright-field illumination anddark-field illumination can be made, its construction is optional and analready present construction may be properly selected and used.

[0112] Besides, kinds of the light source and the light detection meansare not particularly limited, for example, a light source and lightdetection means used in an already present calorimeter may be employedto construct a surface inspection apparatus for measuring color. As thealready present calorimeter, for example, there are minute surfacespectro-colorimeter MSP-Σ90 made by NIPPON DENSHOKUKOGYO CO., LTD., andso on.

[0113] By this manner, the light quantity of the object to be measuredis obtained as a standardized value, in concrete words, the color of thesurface of the object to be measured can be specified with L*a*b* colorsystem, XYZ color system, or the like.

[0114] Otherwise, a light source and light detection means used in analready present lightness meter may be employed to construct a surfaceinspection apparatus for measuring lightness. By this, the lightquantity of the object to be measured is obtained as a standardizedlightness value.

[0115] After all, the kind and construction of the light detection meansare not particularly limited if it can obtain the light quantity of thereceived light.

[0116] Besides, although the electric current value or the value intowhich the electric current value is converted is digitally displayed bythe display means in the above embodiment, it may be displayed in ananalogue form.

[0117] Although the surface inspection apparatus is constructed by usingthe already present polarizing microscope in the above embodiment,without using this polarizing microscope, the surface inspectionapparatus may be constructed by assembling each part such as the lightsource, objective lens, light detection means and slit, etc.

[0118] Further, in the present invention, optical fiber cables can beutilized as follows.

[0119] That is, although the objective lens barrel 33 is used in theabove embodiment, the objective lens barrel 33 can be changed to opticalfiber cables. In this case, the light from the light source isintroduced to optical fibers by a condensing lens. The optical fibercables may be properly selected from among those used in general. Forexample, there are ones that the same quantity of plural fine opticalfibers is bundled into each cable, respectively, and ones that one thickoptical fiber is used as each cable. The optical fibers may be used incommon for transmitting and receiving, but it is desirable to use themin the manner that ones for transmitting and ones for receiving aredistinguished from each other. In this case, the optical fibers on thelight source side, in order that the light condensed through thecondensing lens from the light source enter, and in order to introduceonly the light through the optical fibers for receiving in the reflectedlight from the object to be measured to the slit, the optical fibers fortransmitting and receiving are desirably used with being bundled,respectively. On the other hand, on the object-to-be-measured side, inorder that the light applied to the object to be measured from theoptical fibers and the reflected light entering the optical fibers fromthe object to be measured are evenly distributed within the measurementextent, it is desirable randomly to bundle the optical fibers fortransmitting and receiving, respectively. In case of using a pluralityof optical fibers in the manner that ones for transmitting and ones forreceiving are distinguished from each other, there is no particularlimit in the proportion of the numbers used respectively but it isdesirable to use almost the same number of optical fibers. Besides, itis desirable to attach tubular attachments to the other ends of theoptical fibers. By contacting the tips of the attachments with thesurface of the object to be measured, the measurement can be performedwith keeping constant the distance from the object to be measured or theirradiation angle of the object to be measured with the light. The shapeof the attachment is not particularly limited if it is a shape that thelight applied from the optical fibers reaches the surface of the objectto be measured and the reflected light reaches the optical fibers, andmay be cylindrical, fanwise, or a skeleton construction that the wallsurface of a cylinder is open.

[0120] Besides, the objective lens barrel 33 may be attached to the tipsof the optical fibers for measuring the surface condition with a stillhigher accuracy. Even in this case, it is desirable to attach the aboveattachment to the tip of the objective lens barrel 33.

[0121] By using such flexible and long optical fibers, without puttingthe object to be measured on the stage 21, its surface condition can bemeasured. Accordingly, the measurement is possible independently of thesize of the object to be measured and the place of measurement. Forexample, even a particularly large-sized final product, or one being ata job site such as a factory at a long distance from the main body ofthe measurement apparatus can be measured.

[0122] Further, if a network of optical fiber cables is laid in advancein a wide area such as a laboratory and a factory, if the measurementpart comprising the optical fibers and the attachments, and, accordingto circumstances, the objective lens barrel is separately manufacturedto be portable, it is also possible freely to measure in the network.Otherwise, if the measurement apparatus itself is constructed compactly,it is also possible to provide a portable handy-type measurementapparatus.

[0123] In case of carrying it using the optical fibers, the measurementis possible independently of the size of the object to be measured andthe place of measurement. By attaching the attachments to its mostheaded end, it is also possible to provide a portable handy-typemeasurement apparatus.

[0124] Besides, the objective lens attached to the objective lens barrel33 may be a plane lens of the magnification of 1. In case of themagnification of 1, the objective lens itself becomes needless, but itis desirable to attach the plane glass to the attachment position of theobjective lens for protecting the light source 11 and the lightdetection means 13 from dust and other substances floating in air.

[0125] The kind of the object to be measured, in concrete words, thequality of the material, shape, size, color, or the like is optional.

EXAMPLE

[0126] Using samples made of a synthetic resin as the object 2 to bemeasured in the above embodiment, gloss of injury, unevenness in glossand external appearance of weld line were evaluated, respectively.

[0127] [Evaluation of Gloss of Injury]

[0128] Evaluations of gloss of injury were made on four samples A to Dprovided with different injuries from one another.

[0129] The sample A was obtained in the manner that a flat-boardliketest piece (120 mm×120 mm×3 mm) made of a polypropylene resincomposition in which 23 wt. % of talc, 4 wt. % of ethylene-propyleneelastomer and 1.3 wt. % of a pigment (dark gray) were mixed, wasprepared and an injury of a length of 50 mm was inflicted on this testpiece with a taper scratch tester made by TOYO SEIKI, LTD.

[0130] Inflicting the injury on the test piece was performed by using acylindrical metal stick of a diameter of 3 mm, the outer circumferenceof the tip surface of which was beveled in 4 mmR, in place of a cutterfor inflicting, with applying a load of 20 gf. When the injury isinflicted with such a metal stick, the injured portion becomes smoothand the glossiness becomes higher than that before it is injured.

[0131] The sample B was obtained in the same manner as the sample A butapplying a load of 100 gf when an injury was inflicted on the testpiece.

[0132] The sample C was obtained in the same manner as the sample A butapplying a load of 300 gf when an injury was inflicted on the testpiece.

[0133] The sample D was obtained in the same manner as the sample A butapplying a load of 500 gf when an injury was inflicted on the testpiece.

[0134] <Measurement Example>

[0135] As for these four samples A to D, surface inspections wereperformed with the surface inspection apparatus 1 of the aboveembodiment. These inspections were performed respectively to the injuredportion on which the injury had been inflicted and an uninjured portionwhere there was no injury, in each surface of the samples A to D. Themeasurement conditions were as follows;

[0136] magnification of objective lens: 5

[0137] opening of slit: circle of diameter of 2 mm

[0138] kind of illumination: dark-field illumination (irradiation angleof 45 degrees).

[0139] In these inspections, detected light quantities were displayed asfollows. That is, an inspection of a white standard board was performedin advance under the same measurement conditions as the samples A to D,and the detected light quantity of the white standard board was used asa standard value, and the light quantities detected in the inspectionsof the samples A to D were converted with considering the standard valuethe base of 100%, and displayed. The results are shown in a table 1.

[0140] <Comparative Example>

[0141] On the other hand, measurements were performed respectively onthe injured portions and the uninjured portions of each of the samples Ato D by the method of the Japanese Patent Publication No. 52160/1995,and the light quantities of the reflected lights were obtained asexposure times of a camera. The results are shown in the table 1.

[0142] Injury's hardness to be conspicuous was evaluated on each of thesamples A to D by eye observation, and ranked in order of the hardnessto be conspicuous decreasing. The results are shown in the table 1.TABLE 1 Order of Comparative example hardness Exposure ExposureDifference to be time of time of in Measurement example Injuringconspicuous uninjured injured exposure Uninjured Injured load by eyeportion portion time portion portion Difference (gf) observation (sec)(sec) (%) (%) (%) (%) A  20 1 10 10 0 7.0 6.7 0.3 B 100 2 10 10 0 6.86.4 0.4 C 300 3 10 10 0 6.4 5.7 0.7 D 500 4 10 10 0 7.1 6.0 0.9

[0143] As shown in the table 1, it is understood that, by performing thesurface inspection with the surface inspection apparatus 1 of the aboveembodiment, the difference in gloss between the injured portion and theuninjured portion can be clearly detected and a highly accurateinspection result corresponding to the eye observation result can beobtained.

[0144] On the other hand, by the method of the Japanese PatentPublication No. 52160/1995, there was found no difference in exposuretime between the injured portion and the uninjured portion, and nocorrelation with the eye observation result was obtained. It is thusunderstood that the method of the above embodiment can realize a surfaceinspection with a higher accuracy than the method of the Japanese PatentPublication No. 52160/1995.

[0145] [Evaluation of Unevenness in Gloss]

[0146] Evaluations of unevenness in gloss were made with the surfaceinspection apparatus 1 of the above embodiment on car bumpersmanufactured by injection molding with the same resin as theabove-mentioned samples A to D.

[0147] That is, three bumpers were prepared as samples E to G, and anextent of 13 mm×31 mm including an unevenness portion in gloss arisingon the lower side of a logo formed on each of the samples E to G, thatis, on the lower side of the resin flow, was used as a measurementregion. These measurement regions were at the same position as oneanother in the samples E to G.

[0148] The measurement conditions were as follows;

[0149] magnification of objective lens: 5

[0150] opening of slit: circle of diameter of 5 mm

[0151] kind of illumination: bright-field illumination (irradiationangle of zero degrees).

[0152] In these inspections, the light detection extent by the surfaceinspection apparatus 1 was narrowed into an extent of 1 mm square withinthe above-mentioned measurement region, and the surface in themeasurement region was scanned by inspecting by the extents of 1 mmsquare with intermittently moving the sample 1 mm at a time. Thedetected light quantities were displayed after converting into the rates(%) when the light quantity of the white standard board (standardsample) was 100%, like the above-mentioned samples A to D.

[0153] The maximum value, the minimum value and the difference betweenthem in each measurement region of the samples E to G are shown in atable 2. TABLE 2 Maximum value Minimum value Difference (%) (%) (%)Sample E 11.0 6.3 4.7 Sample F 14.7 6.1 8.6 Sample G 10.7 5.0 5.7

[0154] As shown in the table 2, from the fact that the differencebetween the maximum value and the minimum value in the measurementregion of the sample E is little in comparison with those of the samplesF and G, it is understood that the sample E is a sample of a littleunevenness in gloss. On the other hand, the difference between themaximum value and the minimum value of the sample G is the greatestamong the three samples E to G, and it is understood that it is a sampleof a great unevenness in gloss.

[0155] In this manner, it is understood that, by performing the surfaceinspection with the surface inspection apparatus 1 of this embodiment,the unevenness in gloss in a predetermined measurement region can bemeasured with a high accuracy.

[0156] [Evaluation of External Appearance of Weld Line]

[0157] Evaluations of external appearance of weld line were made withthe surface inspection apparatus 1 of the above embodiment onflat-boardlike samples H and I on the surfaces of which crimps (patternby unevenness in height) are given. These samples H and I were made ofmolds by injection molding in the middles of which rectilinear weldlines were formed, and the sample H has a conspicuous weld line and thesample I has a hardly conspicuous weld line. The measurement conditionsin these inspections were as follows;

[0158] magnification of objective lens: 5

[0159] opening of slit: circle of diameter of 5 mm

[0160] kind of illumination: bright-field illumination (irradiationangle of zero degrees).

[0161] In these inspections, a region of 20 mm×1 mm perpendicularlyintersecting the weld line was used as a measurement region in eachsurface of the samples H and I, and the weld lines were positioned inthe middle portions of the measurement regions, respectively. Themeasurement regions of the samples H and I were set up to be at the sameposition as each other.

[0162] The surface inspection on each measurement region was performedby scanning with moving the samples H and I similarly to the time ofperforming the above-mentioned evaluations of unevenness in gloss(samples E to G). That is, the light detection extents in the surfacesof the samples H and I were narrowed into extents of 1 mm square, andthe inspection was performed by the extents of 1 mm square withintermittently moving the sample 1 mm at a time in the longitudinaldirection of the measurement region, that is, rectilinearly in thedirection perpendicular to the weld line.

[0163] In these inspections, the detected light quantities weredisplayed after converting into the rates (%) when the light quantity ofthe white standard board (standard sample) was 100%, like theabove-mentioned samples A to D and E to G. The results are shown in FIG.4.

[0164] By FIG. 4, it is understood that the reflected light on thesurface of the sample H varies more widely than that of the sample I andthe weld line of the sample H is more conspicuous than that of thesample I. In this manner, it is understood that, by performing thesurface inspection with the surface inspection apparatus 1 of thisembodiment, the external appearance of the weld line, that is, easinessto be conspicuous can be detected as a difference in reflected lightfrom the peripheral portion and a highly accuracy inspection resultcorresponding to the eye observation result can be obtained.

Possibility of Industrial Utilization

[0165] As described above, according to the present invention, byproviding a slit in the optical path between an objective lens forreceiving a reflected light reflected on a surface of an object to bemeasured, and light detection means for detecting a component incidenton this objective lens in a parallel direction with its optical axis,and obtaining its light quantity, and taking out only a component havingpassed through an opening of the slit to detect, because the detectionextent of the reflected light in the surface of the object to bemeasured, that is, the light detection extent can be restricted with theopening of the slit, the surface condition can be measured exactly andwith a high accuracy.

[0166] Further, even in case of using the objective lens of a lowmagnification, because the detection extent in the surface of the objectto be measured can be restricted by the slit, since the surface of theobject to be measured can be finely divided into a plurality of lightdetection extents and detected, the surface condition of the object tobe measured can be measured with a good accuracy.

[0167] Besides, because a superior detection accuracy can be obtained,not only the conventional degree of whitening of an injury but also adifference in the surface condition due to gloss, color, unevenness inheight, or the like can be measured, and because the whole of thesurface of the object to be measured including an uninjured portion canbe measured, in addition to that an evaluation result corresponding tothe external appearance of the object to be measured can be obtained,since it is avoided to inflict a predetermined injury on the surface ofthe object to be measured for measurement as a conventional manner, itcan be applied to not only a surface inspection of a material but also asurface inspection in quality inspection of products.

1. A surface inspection apparatus characterized by comprising a lightsource for applying a light to a surface of an object to be measured, anobjective lens opposite to the surface of said object to be measured andfor receiving a reflected light applied from said light source andreflected on the surface of said object to be measured, light detectionmeans for detecting a component incident on the corresponding objectivelens from a parallel direction with its optical axis in the reflectedlight received by this objective lens and obtaining its light quantity,and a slit provided in the optical path between said objective lens andlight detection means.
 2. A surface inspection apparatus described inclaim 1, characterized in that illumination switchover means is providedin the light path between said light source and object to be measured,and this illumination switchover means is to switch over bright-fieldillumination in which the light from said light source is made parallelwith the optical axis of said objective lens and applied to said objectto be measured through said objective lens, and dark-field illuminationin which the light from said light source is made ringlike and appliedobliquely with respect to the optical axis of said objective lens suchthat there is a focus on the surface of said object to be measured.
 3. Asurface inspection apparatus described in claim 1 or 2, characterized inthat the size of an opening of said slit is changeable.
 4. A surfaceinspection apparatus described in any of claims 1 to 3, characterized inthat said light detection means comprises calculation means forconverting the light quantity of the light having passed through saidslit on the basis of a light quantity detected when a standard sample isused as said object to be measured.
 5. A surface inspection methodcharacterized in that a surface of an object to be measured isirradiated with a light and the irradiation light is reflected on thesurface of said object to be measured, in this reflected light, acomponent parallel with the optical axis of an objective lens providedoppositely to said object to be measured is made incident on a slitthrough said objective lens, in this incident light, only a componenthaving passed through an opening of said slit is received, and the lightquantity of this received light is obtained.
 6. A surface inspectionmethod described in claim 5, characterized in that a light detectionextent in the surface of said object to be measured is controlled bychanging the size of the opening of said slit and the magnification ofsaid objective lens, respectively.
 7. A surface inspection methoddescribed in claim 5 or 6, characterized in that the light quantity ofsaid received light is converted on the basis of a light quantitydetected when a standard sample is used as said object to be measured.8. A surface inspection method described in claim 7, characterized inthat the irradiation angle with the light to said object to be measuredis varied according to the surface condition of said object to bemeasured.
 9. A surface inspection apparatus characterized by comprisinga light source for applying a light to a surface of an object to bemeasured, a tubular member opposite to the surface of said object to bemeasured and for receiving a reflected light applied from said lightsource and reflected on the surface of said object to be measured, lightdetection means for detecting a component incident on this tubularmember from a specified direction in the reflected light and obtainingits light quantity, and a slit provided in the optical path between saidtubular member and light detection means.
 10. A surface inspectionapparatus described in claim 1, characterized in that the tubular memberis an optical fiber cable.
 11. A surface inspection method characterizedin that a surface of an object to be measured is irradiated with a lightand the irradiation light is reflected on the surface of said object tobe measured, in this reflected light, only a component in almost onedirection is made incident on a slit through the tubular member, and, inthis incident light, the light quantity of only a component havingpassed through an opening of said slit is obtained.
 12. A surfaceinspection method characterized in that a surface of an object to bemeasured is irradiated with a light and the irradiation light isreflected on the surface of said object to be measured, this reflectedlight is made incident on a slit through an optical fiber cable, and, inthis incident light, the light quantity of only a component havingpassed through an opening of said slit is obtained.